Normal cells in culture require factors, usually derived from the serum supplement to the medium, for proliferation and survival. When these cells are deprived of serum, they go into a quiescent state from which they emerge if serum is restored. It is widely believed that this represents the recognition of growth stimulatory signals present in the serum supplement. When these cells are transformed by viruses or chemicals, they generally show much less requirement for these growth factors and hormones. They grow at optimal rates in concentrations of serum much lower than that required by their untransformed counterparts and, upon serum deprivation, may even attempt to continue to grow. Only rarely can they be observed to be properly quiescent. The goal of this project is the elucidation of the mode of action of these growth regulatory hormones and factors as they act on normal, fibroblastic cell lines in vitro and the relationship between the loss of these requirements and the acquisition of a malignant phenotype. The nature of these signals and the biochemical mechanisms by which they exert their actions are not known. The recent development of defined, serum-free media supplemented with purified growth factors and hormones will allow the elucidation of the mode of action of these specific growth regulatory compounds. High resolution cytofluorimetric analysis of the DNA distributions of both synchronized and nonsynchronized populations will allow a more accurate determination to be made about the cell cycle specificity of these factors. This will then be extended to a biochemical analysis of the mechanism of hormone action, including identification of the receptors and transducers of the signals. This will be combined with an analysis of several related cell lines, selected specifically for transformed and tumorigenic properties, to determine the mechanism of loss of growth factor responsiveness and its relationship to malignancy. From this, in vivo models may be developed that will aid in an understanding of the development of malignant disease.